The production of glass by the float glass process is well known in the art. Generally, the float glass process involves mixing and heating various components of a glass composition to produce a glass melt, pouring the glass melt onto a bath of molten tin, and drawing the glass melt along the bath of molten tin to form a dimensionally stable continuous sheet of glass.
Various components are added to the glass composition to yield glass having different properties such as color, solar absorbance, strength, etc. The end use of the glass determines the specific components required in the glass composition. For example, in one instance, blue glass may be required so certain components will be used in the composition. In another instance, green glass having a specific UV absorbance may be required so different additives will be used to make up the composition.
A component present in the glass melt is water. At the stage of the float glass process when the glass melt is poured into a tin bath, some of the water diffuses out of the glass melt and dissociates into hydrogen and oxygen at the glass-tin interface. The tin, which has a very low solubility for hydrogen, is basically saturated with hydrogen from the bath atmosphere so very little extra hydrogen can be dissolved in the tin. Consequently, hydrogen from the disassociation of water gets trapped at the interface between the molten glass and tin and ultimately impinges on the bottom surface of the glass appearing as open bottom bubble defects in the bottom surface of a glass article. The open-bottom bubbles can be described as voids in the glass which generally have an inverted-U shape cross-section. The presence of open bottom bubbles increases the overall defect density of the glass.
Customers set requirements for the defect density of glass for certain applications. The standards are very difficult to meet with conventional float glass processes due to the presence of open bottom bubbles.
The present invention provides a novel method for reducing the open-bottom bubble defect density of glass produced in a float glass process, especially an oxy-fuel fired furnace.